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10.410-11 · Infectious Disease and Immunity

Antibodies & Vaccination — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

10 min read 19 parts Lesson 10 of 21 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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10.4 Antibodies and Vaccination — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Relate antibody structure to function, distinguish types of immunity, explain vaccination and outline monoclonal antibodies.Chains — four polypeptide chains (two heavy and two light) hel…

  • Glycoprotein
  • Binding sites
  • Variable region
  • Constant region
  • Agglutination
  • Neutralisation

Part 1 of 9Antibody structure

Antibody structure
Chains
  • Chains four polypeptide chains held by disulfide bonds give a quaternary structure and a Y shape.
    • (two heavy and two light)
Glycoprotein
  • Glycoprotein carbohydrate attached to the heavy chains makes antibodies glycoproteins.
Binding sites
  • Binding sites each antibody has two identical antigen-binding sites, so it can bind two antigens.
Variable region
  • Variable region it has a unique 3-D shape complementary to one antigen.
Constant region
  • Constant region it binds phagocytes.
Hinge
  • Hinge it gives flexibility.
Epitope
  • Epitope the specific region of an antigen to which the binding site attaches.
  • One large antigen may carry several epitopes, each recognised by a different antibody.

Part 2 of 9Antibody actions

Agglutination
  • Agglutination antibodies cross-link pathogens into clumps that are easier to engulf and cannot spread.
Neutralisation
  • Neutralisation antitoxins bind toxins, and other antibodies block binding sites so viruses cannot enter host cells.
Opsonisation
  • Opsonisation antibodies coat pathogens so phagocytes recognise them.
  • Phagocytes have receptors for the constant region.
Complement
  • Complement antibodies trigger lysis through complement.
Immobilisation
  • Immobilisation antibodies bind bacterial flagella, slowing the bacteria so phagocytes catch them more easily.

Part 3 of 9Types of immunity

Types of immunity
Active immunity
  • Active immunity it involves clonal selection and expansion and makes memory cells.
Passive immunity
  • Passive immunity it gives immediate but temporary protection because the antibodies are broken down.
Natural versus artificial
  • Natural versus artificial vaccination gives artificial active immunity.

Part 4 of 9Vaccines

Content
  • Content a vaccine contains antigens but cannot cause disease; boosters increase memory cell numbers.
Live attenuated vaccines
  • Live attenuated vaccines weakened whole pathogens that multiply only slowly without causing disease.
    • (for example MMR)
  • They give a strong, long-lasting response, often after one dose.
  • They are unsafe for people with weakened immune systems.
Inactivated vaccines
  • Inactivated vaccines killed whole pathogens or parts such as proteins or toxoids (for example diphtheria).
    • (for example the polio injection)
  • They cannot cause disease.
  • The response is weaker, so boosters and sometimes adjuvants are needed.

Part 5 of 9How vaccination gives immunity

1
A vaccine containing antigen is injected.
2
Antigen-presenting cells present the antigen to specific helper T-cells and B-cells.
3
Clonal selection and expansion occur (primary response).
4
Plasma cells make antibodies and memory cells form.
5
On later infection memory cells divide rapidly.
6
Large quantities of antibody destroy the pathogen before symptoms (secondary response).

Part 6 of 9Vaccination programmes

Best targets
  • Best targets diseases with a single stable antigen and no animal reservoir, such as smallpox.
    • (ring vaccination)
Smallpox eradication
  • Smallpox eradication the virus was stable, the vaccine was live and easy to store, and symptoms were easy to identify.
Herd immunity threshold ≈ 1 − 1/R0; for measles R0 ≈ 15, so about 93 to 95 per cent coverage is needed.
Measles
  • Measles it still occurs because the vaccine needs two doses and very high coverage, and some parents refuse vaccination.

Part 7 of 9Why some vaccines are hard

1Antigenic variation
  • Antigenic variation influenza and HIV change their antigens.
2Hidden pathogens
  • Hidden pathogens those inside cells, infecting immune cells or in the gut lumen (cholera) escape antibodies.
    • (HIV in helper T-cells)
3Other problems
  • Other problems many strains, poor response in malnourished people, cold-chain storage and public refusal.
4Cholera, malaria and influenza
  • Cholera, malaria and influenza vaccines are hard to produce for these reasons.

Part 8 of 9Making monoclonal antibodies

1
Inject a mouse with the antigen so its B-cells make plasma cells.
2
Extract plasma cells from the mouse spleen.
3
Fuse them with myeloma cells to form hybridomas (using polyethylene glycol or an electric pulse).
4
Culture hybridomas in a selective medium where unfused cells die.
5
Screen the surviving clones to find the one making the required antibody.
6
Grow that clone in large quantities.
7
Collect and purify the monoclonal antibodies.

Part 9 of 9Uses of monoclonal antibodies

Reason for fusion
  • Reason for fusion plasma cells cannot divide, so fusing them with myeloma cells gives hybridomas that both divide and secrete one specific antibody.
Diagnosis
  • Diagnosis pregnancy tests, detecting HIV and locating tumours.
Treatment
  • Treatment for example trastuzumab (Herceptin) for HER2-positive breast cancer, and delivering drugs to cancer cells.
Humanised antibodies
  • Humanised antibodies mouse antibodies are themselves foreign antigens, so they are humanised to reduce the patient's immune response.

Key terms

TermMeaning
AntibodyA Y-shaped glycoprotein with specific variable regions that binds an antigen.
EpitopeThe region of an antigen that an antibody binds.
HybridomaA fusion of a plasma cell and a myeloma cell that divides and secretes one antibody.
Herd immunityProtection of a population when most individuals are immune.
Attenuated vaccineA vaccine of weakened live pathogens.
AdjuvantA substance that boosts the response to a vaccine.

Avoid these mistakes

1
Saying antibodies are made by T cells — plasma cells (B cells) make them.
2
Saying passive immunity gives memory cells — it does not and it is temporary.
3
Saying live vaccines are safe for everyone — they are unsafe for people with weak immune systems.
4
Saying herd immunity needs 100 per cent vaccination — the threshold is about 1 − 1/R_{0}.

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